1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member. More particularly, the present invention relates to an electrophotographic photosensitive member comprising a photosensitive layer which contains a resin having a specified structure and a charge-transporting substance having a specified structure and a specified oxidation potential. The present invention further relates to an electrophotographic apparatus, a device unit, and a facsimile machine employing the above electrophotographic photosensitive member.
2. Related Background Art
In recent years, many electrophotographic photosensitive members have been reported and practically used which employ an organic photoconductive material which is a non-pollutant and permits high productivity, ease of material design, and future possibilities. These electrophotographic photosensitive members are naturally required to have suitable electric characteristics, suitable mechanical characteristics, and suitable optical characteristics for the electrophotographic process to which they are applied.
Since, a photosensitive member which is used repeatedly is exposed at the surface thereof repeatedly to electric and mechanical external forces such as corona discharge, toner development, image transfer to paper, and cleaning treatment, it is therefore required to have durability against these external forms. More specifically, the photosensitive member is required to be resistant to deterioration of characteristics caused by ozone generated at corona charging; namely deterioration of sensitivity, decrease of the surface potential and increase of the residual potential. The member should be resistant to abrasion and scratching of its surface caused by sliding elements on such surface during image transfer and cleaning.
The surface of the photosensitive member is usually constructed of an extremely thin resin layer, and the properties of the resin employed is one of the factors affecting greatly the electrophotographic characteristics of the photosensitive member. The resins which meet the above requirements and are conventionally used for the photosensitive member include a polycarbonate which is synthesized from a bisphenol having a 2,2-propylidene portion in the skeleton (hereinafter referred to as polycarbonate A), and a polycarbonate which is synthesized from a bisphenol having a cyclohexylidene portion in the skeleton (hereinafter referred to as polycarbonate Z).
The photosensitive member is usually formed by dispersing or dissolving a charge-generating substance or a charge-transporting substance, applying the resulting dispersion or solution on a support, and drying the applied matter. The resin film, especially a polycarbonate resin film, formed through such steps as above generally has residual stress in its internal structure, and is liable to cause solvent cracks disadvantageously. Thereby, on contact with a finger or oil during handling or fitting the member to an electrophotographic apparatus, the electrophotographic photosensitive member may develop cracks in the photosensitive layer. The formed cracks in the resin film may cause defects in the developed image.
With recent demand for high quality images and high durability of photosensitive members, electrophotographic photosensitive members have been studied for better solvent resistance in addition to electrophotographic characteristics.